Abstract. The ISO and IUE spectra of the elliptical nebula NGC 5315 is presented. These spectra are combined with the spectra in the visual wavelength region to obtain a complete, extinction corrected, spectrum. The chemical composition of the nebulae is then calculated and compared to previous determinations. The HST NICMOS observations of the nebula in 3 emission lines are also presented. These observations are used to determine the helium abundance as a function of position in the nebula. A discussion is given of possible evolutionary effects.
NGC 7027 is the brightest planetary nebula (PN) in the sky despite the fact that it is dimmed by 14 db (i.e., about 3.5 magnitudes) of local and interstellar extinction. It is also one of the intrinsically most dense and luminous of PN, although it may have evolved from a progenitor in the 1.5-5 9K 0 range. Observations secured with the Hamilton echelle spectrograph at Lick Observatory and with the IUE are analyzed to obtain nebular plasma diagnostics and chemical abundances. Much of the nebular plasma seems to have a density N e ~ 60,000 cm 3 and temperature T e ~ 14,000 K, although the [Ne iv] and [Ar iv] auroral/nebular line ratios suggest a N e ~ 54,000 cm 3 and T e ^ 16,000 K zone, while [S n] suggests a zone at N e ^ 30,000 cm 3 , T e ~ 13,000 K. Nebular models based on currently available theoretical stellar fluxes for hot stars (T ~ 180,000 K to 200,000 K) predict He II X4686 too strong and [Ne v] too weak. It is suggested that the stellar radiation field is greatly enhanced shortward of 130 A because of a dense non-LTE wind. The chemical composition appears to be that of a "normal" carbon-rich object rather than that of a nitrogen-rich object such as NGC 2440, which presumably had a massive progenitor.
We have obtained the first high-dispersion observations of RX Pup in the wavelength region 1200-2000 A with the International Ultraviolet Explorer. RX Pup has been classified a symbiotic star and has been compared to slow novae as well as to 11 Carinae. The anomalies that we observed in high-excitation lines in RX Pup such as He II, 0 III], C III], C IV, and Si IIIl that show split line profiles, Doppler displaced multiple components, and possible inverse P Cygni profiles inN III] and N IV J suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum observed by us in low dispersion is fairly flat in the wavelength region 1200-2000 A and rises toward longer wavelengths in the region 2000-3200 A. It cannot be due to a star earlier than AO II. Alternatively it may be from an accretion disk. We find electron densities in the line-emitting region in the range 10 9-10 11 em-3 , temperatures in the range 10,000-20,000 K, and linear sizes :S a few x 10 13 em. We find that the photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature in the range 75,000-90,000 K. Alternatively it may be due to an accretion disk around a secondary with boundary layer temperature-10 5 K. Short-range as well as long-range monitoring of this very interesting object in the far-UV would be very helpful in understanding the nature of its peculiar properties and the connection between slow novae and symbiotic stars.
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